Finding array(s) of pixel coordinates of pixels contained in an ROI

[Saamic]

So, I am currently writing code that the gives the percent of pixels shared between two ROIs. I am trying to fill an array (or 2 arrays, an x array whose entries correspond with a y array's entries) with the coordinates of pixels that are enclosed by one of the ROIs (drawn using the polygon tool), however I am unaware of the code that I have to implement to do so. Could someone please tell me how I could develop/retrieve such an array?